3 ms·

When that's your title and your first paragraph has at least 2 errors in it, how likely am I to believe what you say in the rest of the piece? $25 does not get

• michaelt 14y ago
  >700mA on USB is not within the USB spec, and probably not accurate for current draw of a Pi. The raspberry pi quickstart guide at http://www.raspberrypi.org/quick-start-guide http://www.raspberrypi.org/quick-start-guide says to use a power supply capable of supplying 700 mA. The page you link to says the RPi can consume 435-465mA just from CPU and Ethernet, meaning only ~250 mA of the RPi's 700mA power budget remains to power the two USB host ports. Just plug in a USB device that draws more than 250mA (like a second RPi) and the claim of consuming more than 700 mA will be proved correct!
  • gravitronic 14y ago
    If you plug a USB device that consumes more than 100mA into the pi it will likely not power the usb device without a powered hub in between.
    • michaelt 14y ago
      I've checked the RPi schematic [1] and it each of the USB ports protected by a miniSMDC014 rated for 140 milliamps [2] (and taking 150ms to trip at 1.5 A) With two usb devices drawing 140 mA, a total of 280 mA would be consumed, thereby narrowly exceeding the 700mA power budget. Fuses are also typically quite imprecise for obvious reasons - they rely on current heating up metal that melts and breaks the circuit, and you don't want it borderline molten under normal operating conditions! So you may well be able to draw 250 mA per port without the fuses triggering. You'll note the Raspberry Pi wiki [3] has a bunch of bug reports like "Ethernet connection is lost when a USB device is plugged in" attributed to inadequate power supply current. [1] http://www.raspberrypi.org/archives/1090 http://www.raspberrypi.org/archives/1090 [2] http://datasheet.octopart.com/MINISMDC014F-2-Tyco-Electronics-datasheet-58412.pdf http://datasheet.octopart.com/MINISMDC014F-2-Tyco-Electronic... [3] http://elinux.org/R-Pi_Troubleshooting http://elinux.org/R-Pi_Troubleshooting
      • gravitronic 14y ago
        So, I've got one and am experiencing similar issues.. I believe that right now the "power supply" issue had been used as a blanket response to ethernet/usb issues until people were seeing that problem with an oscilloscope on their power supply and no power supply issues. What seems to be the common conclusion is that it's a bug in the DWC OTG USB driver/firmware: http://www.raspberrypi.org/phpBB3/viewtopic.php?t=9470&p=128799 http://www.raspberrypi.org/phpBB3/viewtopic.php?t=9470&p... et al
• shanselman 14y ago
  A minimum of 700mA on USB is absolutely what a Raspberry PI takes and is listed as such on their website. Their site also says that each of their USBs port can handle only 100mA, and little more. [1] "Generally speaking the model B raspberry PI was designed only for <100mA USB devices! That is because the PI's PSU was chosen with a power budget of 700mA in mind of which 200mA were assigned to the two USB ports, so the raspberry PI's (poly)fuses were designed only for <100mA devices, and typical 140mA polyfuses will have as much as 0.6 volt across them when drawing currents near the 100mA limit. As a consequence the USB ports are only directly suitable for "single current unit" USB devices which according to USB specifications are designed to work with just 4.4 Volt. Not only do non single current unit devices draw more current, (causing greater Voltage drops, and greater stress on the fuses) they also might require 4.75 Volt to work. Therefore any non single current unit devices will only work when powered from a powered hub." Plugging in devices that take 150mA or more almost always cause problems. Sure these things aren't within the USB spec, but neither is my 2A iPad 3. As for $25 vs. $35, oops. I pre-ordered months ago and had forgotten what I'd paid. [1]:http://elinux.org/RPi_VerifiedPeripherals http://elinux.org/RPi_VerifiedPeripherals